1. Technical Field
The present invention relates generally to a single-shaft two-speed drive system for an electric vehicle, and more particularly to the field of application of a technology for implementing gear reduction ratios based on the gear reduction and direct coupling of planetary gears to an electric vehicle and similar drive systems.
2. Description of the Related Art
Conventional drive units for an electric vehicle are composed of a housing configured to surround a motor, a gear box, and a differential configured to receive the driving power of the gear box. In these conventional drive units, the gear box and the differential are disposed on separate shafts. There are many cases where the power transmission path of a drive unit for an electric vehicle is composed of two shafts. A motor composed of a rotor and a stator is disposed inside a housing, one end of a first shaft is coupled to be operated in conjunction with the rotor, the other end of the first shaft is coupled to be operated in conjunction with a differential on the same axial line, and the differential is coupled to a gear box having a second shaft of a different phase difference. In connection with this, Korean Patent No. 0195022 entitled “Drive Device for Electric Vehicle” and issued on Feb. 10, 1999 was disclosed. The drive device of this patent is disadvantageous in that a space in which a gear box is installed is limited and overall volume and weight are increased because the drive device of this patent has a structure in which the gear box is required to be disposed outside the housing. Furthermore, the conventional drive units are problematic in that fuel efficiency is decreased because volume and weight are increased due to the structural characteristics of a connection structure that connects multiple shafts.
To overcome the above problems, there was proposed Korean Patent No. 1374872 entitled “Drive Unit Device for Electric Vehicle” and published on Mar. 10, 2014. In the drive unit device of this patent, at least one planetary gear set, a motor, and a differential are densely disposed along the same axial line within a single housing, so that a limitation related to an installation space can be reduced by decreasing the volume of the device, the number of parts and weight can be reduced, and noise and vibration can be reduced due to the characteristic in which the generation of power and gear reduction action are simultaneously performed on the single same axial line. However, the drive unit device of this patent is problematic in that a gear reduction ratio suitable for the inherent characteristic of the planetary gear set can only be passively obtained.